Light-to-electrostatic-image converter and process for manufacturing same



J1me 1965 J. J. STONE ETAL LIGHT-TO-ELECTROSTATIC-IMAGE CONVERTER AND PROCESS FOR MANUFACTURING SAME Filed April 10, 1962 JOSEPH J. S TONE JON/V 1 EOQrQA/D -INVENTORS United States Patent LIGHT-TO-ELECTRGSTATTGEMAGE CGNVERTER AND PRGCESS FOR MANUFAQTURILNG SAME Joseph J. Stone, Glenview, and John H. Harland, Dundee,

Ill, assignors to A. B. Dick Company, Ehicago, TEL, a

corporation of Illinois Filed Apr. 1%, 62, Ser. No. 186,474- 3 Claims. (Cl. se t This invention relates to apparatus for reproducing a light image on paper and, more particularly, to an im provement in apparatus for converting a light image into electrostatic charges on an insulating surface.

The process of reproducing a light image on paper by first converting the light image into a representative electrostatic-charge pattern, depositing pigment powder on those portions of the paper where the charge pattern exists, and then fixing said pigment powder on the paper, is very well known. The apparatus which is employed for converting the light image into the electrostatic-charge pattern may comprise a selenium plate or a plurality of photodiodes. The light image may be directed on the selenium plate, which thereafter is brought in contact with the paper on which the image is to be developed, and the charges on the selenium plate are transferred to said paper. The photoconductive property of photodiodes is used for depositing an electrostatic-charge pattern on the paper. The paper is placed between a conductive ground plate and one surface of the photoconductor, and the light image is made to shine on the other surface of the photoconductor. A potential is applied across the photoconductors. Since the resistance of the photoconductors varies with the amplitude of the light to which they are exposed, a charge pattern is deposited on the paper which represents the light image.

One of the reasons why photoconductors are not finding much use for the electrostatic image-reproducing process is because it is not possible to pack a sufficient number of these together to achieve a line image. Furthermore, photoconductors are expensive, and the expense entailed in putting together a large number of these makes their use prohibitive. There are other problems attendant to assembling photoconductors for the purpose of image reproduction which are of a mechanical nature, that is, the alignment of the photoconductors should be accurate, and some means for properly supporting the photoconductors, while maintaining electrical separation of the discharging portions thereof, is also necessary. The latter problem serves to prevent obtaining a close spacing of the photoconductors.

An object of this invention is the provision of a novel and unique light-to-electrostatic-image converter.

Another object of this invention is the provision of a light-to-electrostatic-image converter which can provide a larger number of photoconductors within a given area than heretofore achievable.

Yet another object of this invention is to provide a light-to-electrostatic-image converter which is simpler to manufacture than heretofore possible.

Still another object of the present invention is to provide a light-to-electrostatic-image converter which is less expensive than those employed heretofore.

These and other objects of the invention are achieved by drilling a plurality of closely spaced holes adjacent one another in a sheet of insulating material, such as glass. A wire is inserted in each one of these holes and finished off flush with the surfaces thereof. Thereafter, the wires in the holes are all etched to a predetermined depth from one surface of the sheet of insulating material. The etched-out holes are then filled with photoconducting material. Thereafter, the surface to which the photocon- Patented June 1, 1965 ducting material extends is covered with a layer of transparent conducting material.

The light-image-to-electrostatic-image converter thus fabricated may then be used in the traditional manner, whereby paper is brought in contact with the surface to which the wire points extend, and the light image is caused to shine upon the surface to which the photoconducting material extends. A potential is applied between the conductive surface and a conductive plate which is positioned on the opposite side of the paper. As a result, an electrostatic image is deposited on the surface of the paper which is representative of the light image which has been directed upon the converter.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:

FIGURE 1 is a perspective view of an embodiment of the invention;

FIGURE 2 is an enlarged section along the lines 2-2 of FTGURE 1;

FIGURE 3 shows how the embodiment of the invention may be employed as an ima e converter; and

FIGURE 4- is another view of how an embodiment of the invention may be employed as a continuous-process image converter.

Reference is now made to FIGURE 1 and FIGURE 2, which respectively show an embodiment of the invention and an enlarged section along the lines 2 thereof. The invention comprises a sheet of insulating material 10, which has therein a plurality of holes 12, which extend through the insulating material. As may be seen in FIGURE 2, each one of these holes is filled with two elements. One of these is the wire 14, which extends from one surface of the insulator inward, and the other of these is a photoconductive material 16, which extends "rom the other surface of the insulator until it connects with the wire. Over the surface to which the photoconductive material etxends there is a transparent conductive layer 1%.

in order to manufacture an image converter in accord ance with this invention, the insulating sheet 1% has a plurality of holes drilled therein which are spaced apart by an amount determined by the density desired for the photodiodes which are formed therein. In an embodiment of the invention, this consisted of 250 holes to the inch. Each one of these holes has a wire inserted therein. The wire is finished oil flush with the surface of the insulating material sheet. Thereafter, the wires are etched from one side of the insulating material sheet to a predetermined depth. The space provided by the etching process is then filled with photoconductive material. The surface of the insulating sheet to which the photoconductive material extends is then coated with a transparent conductive material. In this manner, there is established a plurality of independent photoconductive cells.

In an embodiment of the invention which was built, a glass plate on the order of .0050" thick was used. Holes were drilled to a density of 250 to an inch. The etching of the wires was permitted to proceed to a depth of 10 mils. The photoconductive material which was employed was cadmium sulfide.

FIGURE 3 shows how the embodiment of the invention may be employed in order to convert a light image to an electrostatic image. The converter 20, in accord ance with this invention, is positioned to have the surface to which the wire ends extend in contact with a snseasc a, a paper 22, upon which it is desired to deposit an electrostatic image. A conductive backing plate 24 is placed on the other side of the paper. A high voltage 26 is connected between the transparent conductive backing of the embodiment of the invention and the conductive backing plate 24. When light from the image is caused to be shined upon the transparent conductive coating, a pattern of charges corresponding thereto is deposited on the surface of the paper. This charge pattern may be developed in the manner commonly employed for the xerographic processes by removing the paper from the image converter 2%, dusting its surface with a pigment powder having suitable triboelectric properties, whereby the powder adheres to those portions of the paper which have an electrostatic charge thereon. Thereafter, the pigment powder and paper are treated in a manner to cause the powder to be fixedly attached to the paper. This may be done by the application of heat.

FIGURE 4 shows another arrangement for utilizing an embodiment of this invention. This time, the image converter 3% consists of a bar having a single line of the photoconductors manufactured in the sheet of insulating material. A light image from a source 32 is caused to be scanned across the bar image converter 30. A web of paper 34 is passed between the opposite side of the bar 30, to which the image is applied, and a conductive backing plate 36. A high-voltage source 38 is connected between the conductive coating on the image con verter 3t? and the backing plate 36. The motion of the paper 34 past the image converter is at a speed which is related to the speed with which the image from the light image source 32 is scanned past the converter 30. Thereafter, the paper 34 is passed through an image developer 46. This image developer serves to dust the surface of the paper with a pigment powder, removes pigment powder from those regions of the paper where no charge has been deposited and thereafter fixes the remaining pigment powder to the paper by applying heat thereto.

There has been described hereinabove a novel, simple, and useful converter for converting a light image to an electrostatic image, employing the properties of photoconductive material, whose resistance varies with the intensity of the light applied thereto.

We claim:

1.. An image converter for converting a light image to a charge on a charge receiving member comprising a sheet of insulating material having a hole extending between opposite surfaces of said sheet of insulating material, a conductor in said hole extending from one surface partly to the opposite surface, photoconductive material filling the remainder of said hole, a transparent conductive coating over said opposite surface upon which a light image to be converted is permitted to fall, a conductive member spaced from said one surface by the thickness of said charge receiving member, and means for applying operating po tential between said transparent coating and said conductive member whereby said charge receiving member may receive a charge pattern as determined by said light image.

2. A light-to-elcctrostatic-image converter for converting a light image to a charge on a charge receiving member comprising a sheet of insulating material having a plurality of apertures therein extending from one surface to an opposite surface thereof, said apertures being filled by photoconductive material extending from one surface part way to the opposite surface and conducting material extending from the photoconductive material to the opposite surface, a transparent conductive coating over the surface from which the photoconductive material extends upon which a light image to be converted is permitted to fall, a conductive member spaced from said opposite surface by the thickness of said charge receiving member, and means for applying operating potential between said transparent conductive coating and said conductive member whereby said charge receiving member may receive a charge pattern as determined by said light image.

3. The method of manufacturing a light-t0-electrostatic-image converter comprising drillin a plurality of holes in a sheet of insulating material which extends between opposite surfaces thereof, inserting a conductive wire into each one of said holes, etching away the wire in each one of said holes from one surface in said insulating sheet to a predetermined depth, filling the opening provided by etching with a photoconductive material, and covering the surface from which said photoconductive material extends into each of said holes with a transparent conductive coating.

References Cited by the Examiner UNITED STATES PATENTS 1,880,289 10/32 Sukumyln 96-1 2,65 0,25 8 8/ 53 Pantchechnikofi 3 3 8-15 2,747,104 5/56 Jacobs 338-17 2,777,040 1/57 Kazan 338-17 2,899,659 8/59 Mcllvaine 338-17 2,912,592 11/59 Mayer 338-17 3,007,049 10/61 McNaney 96-1 FORETGN PATENTS 424,914 9/47 Italy.

NORMAN G. TORCHIN, Primary Examiner.

RICHARD M. WOOD, Examiner. 

1. AN IMAGE CONVERTER FOR CONVERTING A LIGHT IMAGE TO A CHARGE ON A CHARGE RECEIVING MEMBER COMPRISING A SHEET OF INSULATING MATERIAL HAVING A HOLE EXTENDING BETWEEN OPPOSITE SURFACES OF SAID SHEET OF INSULATING MATERIAL, A CONDUCTOR IN SAID HOLE EXTENDING FROM ONE SURFACE PARTLY TO THE OPPOSITE SURFACE, PHOTOCONDUCTIVE MATERIAL FILLING THE REMAINDER OF SAID HOLE, A TRANSPARENT CONDUCTIVE COATING OVER SAID OPPOSITE SURFACE UPON WHICH A LIGHT IMAGE TO BE CONVERTED IS PERMITTED TO FALL, A CONDUCTIVE MEMBER SPACED FROM SAID ONE SURFACE BY THE THICKNESS OF SAID CHARGE RECEIVING MEMBER, AND MEANS FOR APPLYING OPERATING POTENTIAL BETWEEN SAID TRANSPARENT COATING AND SAID CONDUCTIVE MEMBER WHEREBY SAID CHARGE RECEIVING MEMBER MAY RECEIVE A CHARGE PATTERN AS DETERMINED BY SAID LIGHT IMAGE. 